Humanize chart units for Value stream analytics

What does this MR do and why?

Humanizes the chart units for Value stream analytics. Instead of using days for units on the overview and duration charts, use human readable units. Seconds/minutes/hours/days will be automatically used interchangeably based on the metric duration.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Ensure you are using GitLab Ultimate
2. Create a new Project
3. Generate mock data: FILTER=customizable_cycle_analytics SEED_CUSTOMIZABLE_CYCLE_ANALYTICS=1 VSA_SEED_PROJECT_ID=${PROJECT_ID} bundle exec rake db:seed_fu
4. Navigate to VSA for the project: Analyze > Value stream analytics
5. View the humanized units for the Overview and Stage charts

Related to #464261 (closed)